Is there any formal guideline that would indicate the necessity for adjustment for baseline when analysing change from baseline? As in the topic. I saw many critical discussions along with mathematical explanation on why the baseline shouldn't (or mustn't) be employed as a covariate, when analysing the change from baseline. From the other side, certain regulators, like those pharmaceutical drug approval bodies, often demand it. Today I am not asking whether it is valid or not, but rather if you saw any formal document, that would address that? At least with a single sentence.
 A: I found one: POINTS TO CONSIDER ON ADJUSTMENT FOR BASELINE COVARIATES
issued by The European Agency for the Evaluation of Medicinal Products
Page 5

II.7.     ‘Change from baseline’ analyses When the analysis is based
on a continuous outcome there is commonly the choice of whether to
use  the  raw  outcome  variable  or  the  change  from  baseline  as
the  primary  endpoint.    Whichever of these endpoints is chosen, the
baseline value should be included as a covariate in the primary
analysis.  The use of change from baseline without adjusting for
baseline does not  generally  constitute  an  appropriate  covariate
adjustment.  Note  that  when  the  baseline  is  included  as  a
covariate  in  the  model,  the  estimated  treatment  effects  are
identical  for  both  ‘change  from  baseline’  and  the  ‘raw
outcome’  analysis.    Consequently  if  the  appropriate  adjustment
is done, then the choice of endpoint becomes solely an issue of
interpretability.

https://www.ema.europa.eu/en/documents/scientific-guideline/points-consider-adjustment-baseline-covariates_en.pdf
Also: Adjusting for Covariates in Randomized Clinical Trials for Drugs and Biologics with Continuous Outcomes Guidance for Industry
This is draft, but describes a common practice.

Many clinical trials use a change from baseline as the primary outcome
measure.  Even when 74 the outcome is measured as a change from
baseline, the baseline value can still be used advantageously as a
covariate

Issued by the FDA
https://www.fda.gov/regulatory-information/search-fda-guidance-documents/adjusting-covariates-randomized-clinical-trials-drugs-and-biologics-continuous-outcomes-guidance
And the summary here: http://onbiostatistics.blogspot.com/2019/05/fda-and-ema-guidance-on-adjusting-for.html
Also:

Source: Guideline on adjustment for baseline covariates in clinical trials
